The typical structure of a CD-R or DVD-R disc includes an energy absorbing dye layer deposited directly over a polymeric substrate. Next, a thin film reflective layer is typically formed directly over the dye layer, usually via magnetron sputtering. This reflective layer also functions as a barrier layer to isolate the dye layer. Finally, a radiation curable protective lacquer is applied directly over the reflective layer.
Because of cumulative stress associated with these various layers, the structure may tend to delaminate, starting at the outermost edge of the substrate. In order to reduce the likelihood of this type of failure, the protective lacquer must bond directly to the substrate surface at the outer edge of the substrate. Additionally, allowing the protective lacquer to bond directly to the polymeric substrate provides an effective barrier to atmospheric contamination of the energy absorbing and reflective layers. Simple masking can be used to shield the outer edge of the substrate during deposition of the reflective layer. However, masking is not practical during the spin coating step used to apply the dye layer. Some means of trimming the dye at the outer edge of the disc is therefore required, as removal of the dye at the outer edge of the disc is advantageous in preventing failure of the coated structure.
Typical approaches to trimming the dye at the outer edge of the disc include solvent "washing" and mechanical trimming operations. Solvent washing, however, requires precise control over the application and spin drying process. In addition, the initial cost of solvent, plus the cost of contaminated solvent disposal are substantial. Mechanical edge trimming is relatively easy to implement. However, debris generation, tooling wear, and proper cooling must be considered. Therefore, it has been found desirable to provide an edge trimming system for an optical memory disc which avoids these limitations and is easily implemented, reliable, and economical.